Processes for converting olefins to aldehydes and/or alcohols by the reaction of an olefin with carbon monoxide and hydrogen in the presence of a suitable catalyst in either batch or continuous processes are well known in the prior art, and are commonly known as oxo or hydroformylation processes. Many of these reactions require the use of exceedingly high pressures to maintain catalyst stability, particularly when a cobalt carbonyl catalyst is employed.
U.S. Pat. No. 3,239,566 to Slaugh et al and similarly, U.S. Pat. Nos. 3,527,809 to Pruett et al and 3,511,880 to Booth, describe processes for the hydroformylation of olefins in which the necessity of using these high pressures is avoided by employing as a catalyst a complex and Group VIII noble metal, carbon monoxide and a ligand. The preferred metal is rhodium, while the ligand is preferably a trivalent organophosphorus compound, especially a phosphite or phosphine. It is disclosed that the catalytic complex may be pre-formed by combining an organic or inorganic salt of the metal with the desired ligand in liquid phase, then reducing the valence state of the metal and forming the metal-containing complex by heating the solution in an atmosphere of admixed hydrogen and carbon monoxide. It is also taught that the reduction may be performed prior to the use of the catalyst or may be accomplished in situ by heating the metal salt in admixture with the ligand in the presence of both hydrogen and carbon monoxide. Also, the catalyst may be formed by heating a rhodium carbonyl with the phosphorus-containing ligand.
Of these alternatives, the most economical and efficient, particularly in a continuous process, is the in situ formation of the catalyst by introduction of the Group VIII metal salt and ligand into the reaction vessel along with the olefin, hydrogen and carbon monoxide. In practice, however, the alternative tends to be of limited practicality when using the economically available inorganic metal salts, especially the water-soluble inorganic salts of rhodium, since a portion of the metal may be reduced by the hydrogen present in the reaction vessel prior to formation of the metal-carbon monoxide-ligand complex. As a result, a precipitate of elemental metal and/or undesirable metal derivatives is formed in the reaction vessel necessitating frequent purging. Moreover, it is necessary to replenish the metal lost in this manner, thus significantly increasing the operational costs of the process.